Brake actuating and adjusting mechanism

ABSTRACT

A brake mechanism having a pressure actuated piston moving disc brake pad assemblies into braking engagement with a disc for service brake operation, and a mechanically actuated mechanism which mechanically moves the piston to engage the brake pad assemblies with the disc for a parking brake operation. The mechanical mechanism includes a one-way lock means mounted on a rotatable and axially movable shaft so that it maintains brake adjustment by sliding on the shaft with excess movement of the piston in the brake engaging direction, but locks on the shaft to prevent movement of the piston in the brake release direction beyond a small predetermined amount sufficient to establish brake pad and disc clearance. The piston is normally nonrotatable in its cylinder, but holding means preventing substantial piston rotation may be released to activate reset means for the one-way lock means so that rotational movement of the piston engages the one-way lock means and prevents it from locking on the shaft so as to permit movement of the piston into the cylinder to reset the piston position when new brake linings have been installed.

United States Patent Brooks [451 Oct. 16, 1973 BRAKE ACTUATING ANDADJUSTING MECHANISM Primary Examiner-Duane A. Reger Attorney-W. S.Pettigrew et al.

[5 7] ABSTRACT A brake mechanism having a pressure actuated pistonmoving disc brake pad assemblies into braking engagement with a disc forservice brake operation, and a mechanically actuated mechanism whichmechanically moves the piston to engage the brake pad assemblies withthe disc for a parking brake operation. The mechanical mechanismincludes a one-way lock means mounted on a rotatable and axially movableshaft so that it maintains brake adjustment by sliding on the shaft withexcess movement of the piston in the brake engaging direction, but lockson the shaft to prevent movement of the piston in the brake releasedirection beyond a small predetermined amount sufficient to establishbrake pad and disc clearance. The piston is normally nonrotatable in itscylinder, but holding means preventing substantial piston rotation maybe released to activate reset means for the oneway lock means so thatrotational movement of the piston engages the one-way lock means andprevents it from locking on the shaft so as to permit movement of thepiston into the cylinder to reset the piston position when new brakelinings have been installed.

2 Claims, 3 Drawing Figures BRAKE ACTUATING AND ADJUSTING MECHANISM Theinvention relates to a mechanism for actuating the brake shoes of apressure actuated disc brake assembly so as to maintain brake adjustmentand to also actuate the brake by manual application to provide a parkingbrake mode of operation. The parking brake mechanism changes rotationalor arcuate motion of an actuated lever to linear motion of the pressureactuated piston, and provides an arrangement for compensating for brakelining wear and also for compensating for brake lining swell or growth.A one-way lock means, mounted on the rotatable and axially movable shaftcontrolled by the manually operated lever, is utilized, the lock meansbeing capable of moving with the piston under normal hydraulic actuationof the brake system, when adjustment is needed to the extent necessaryto engage the shoes with the disc, but locking on the shaft when thepiston is released, so as to prevent substantial return movement of thepiston into the cylinder. This action maintains brake adjustment eachtime the hydraulic mechanism is actuated for service brake operation.When the shaft is rotated by the lever, a suitable mechanism such as aball-ramp actuating device also imparts axial movement to the shaft,moving the locked one-way lock means with the shaft and engaging thelock means with the piston, and then moving the piston axially toactuate the brake system. The piston and its immediately associatedbrake pad assembly are so arranged that the piston cannot rotate to anysubstantial extent in the cylinder. Since the piston is provided with areset mechanism for the lock means, the reset mechanism is actuated byrotational movement of the piston after the associated brake padassembly has been removed. The reset mechanism includes a ramparrangement which engages the one-way lock means so as to position thelock means relative to the shaft so that the lock means can slide on theshaft as the piston is moved inwardly into the cylinder a distancenecessary for installation and use of a new set of brake linings. Thepiston will then be rotated back to its original position, the newlinings installed, and the brake assembly will be rendered ready foroperation. Upon the first hydraulic actuation, the assembly will beproperly adjusted, and it will also be adjusted each time the brakes arehydraulically actuated.

IN THE DRAWING ing purposes by the linings and 22 of the brake padassemblies 24 and 26. The caliper frame 28 is generally U-shaped, with abridge section 30 joining legs 32 and 34. Leg 32 is the outboard leg,and engages the backing plate 36 of the brake pad assembly 24. Thebacking plate 38 of the brake pad assembly 26 is arranged to be engagedby a piston 40, which is reciprocally mounted in a cylinder 42 formed ina housing 44. Housing 44 is suitably secured and mounted in the inboardcaliper frame leg 34. In the particular construction illustrated, anopening 46 receives the housing 44 therethrough, the housing beingprovided with a flange 48 which prevents axially outward movement of thehousing once it is in place. The cylinder 42 opens toward disc 14. Thepiston 40 is suitably sealed to prevent fluid leakage by seal 50, andthe boot 52 prevents contaminants. from entering the cylinder. Thepiston 40 has a head 54 and a skirt section 56 extending from the headand into the cylinder 42. The recess 58 contained within skirt 56 is apart of the pressurizing chamber 60 defined by piston 40, cylinder 42,and the base wall 62 of cylinder 42, which is a part of the housing 44.

The actuating shaft 64 extends through an opening 66 which is axiallyaligned with cylinder 42 and piston 40. Shaft 64 is both rotatable andaxially movable through opening 66, a suitable seal 68 being provided toseal the opening 66 about the shaft 64. The outer end 70 of shaft 64 hassecured thereto an actuating lever 72 which is in turn attached bysuitable means such as a cable to a parking brake control mechanismoperated by the vehicle operator. When the lever 72 is moved arcuately,actuating shaft 64 is rotated. The inner end 74 of actuating shaft 64extends into pressure chamber 60 and recess 58 of piston 40. The pistonhead 54 is provided with a small recess 76 into which shaft end 74 alsoextends. A shoulder 78 separates the portion of actuating shaft 64 whichis contained within opening 66 and an enlarged section 80 whichterminates at shaft inner end-74. Opposed flat surfaces 82 and 84 areprovided on section 80 for purposes to be described. An annular flangemember 86 fits about shaft 64 so that one side abuts against shoulder78. Flange 86 is part of a ball-ramp actuating mechanism 88, and hasdepressions receiving actuator balls 90 therein. Base wall 62 isprovided with ball ramps 92 also receiving balls 90 so that whenrotation of shaft 64 is affected by arcuate movement of lever 72, theballs ride up the ramps, causing the shaft 64 to move axially towardpiston 40. A resilient seal and return element 94 is fixed to housing 44at the exterior end of opening 66 and is also fixed to actuating shaft64. Element 94 not only seals the actuating shaft and opening 66, but,being resilient, also acts as a return spring so that when lever 72 isreleased, there is a return force exerted on shaft 64, causing it tomove axially away from piston 40 and to the position shown in FIG. 1 ofthe drawing. This movement is concurrent with movement of balls 90 backdown ramps 92. v

A one-way locking arrangement is provided between the piston 40 and theactuating shaft 54. The particular locking means disclosed includes alock plate pack formed by a plurality of lock plates, three such plates96, 98 and 100 being illustrated. As is better seen in FIG. 3, the lockplates are generally annular with their respective openings 102, 104 and106 being shaped to conform to the cross-section shape of the enlargedsection 80 of actuating shaft 54, which contains flat surfaces 82 and84. Openings 102, 104 and 106 are formed with their axes at an obliqueangle to the plate axes, and fit shaft enlarged section 80 so that theplates are positioned on the shaft at an oblique angle, in the mannershown in FIG. 1. The openings are also beveled on their opposite sidesso that the arcuate portions of the openings at the upper and lowersides, as seen in FIGS. 1 and 3, have relatively sharp edgepresentations to the surface of the shaft enlarged section 80 but not sosharp as would be the case without the bevels. The spring 108 fits aboutthe lock plate in such a manner that it tends to hold the lock platestogether and urges them toward the perpendicular relative to the axis ofshaft section 80 so that they are locked on the shaft.

A lock plate retainer 110, which may be a snap ring, is fitted withinthe recess 58 formed by piston skirt 56 and is so spaced from the pistonhead 54 as to permit reception of the lock plates generally between thepiston head 54 and the retainer 110. As can be seen in FIG. 1, theannular width along the radius of each of the lock plates 98 and 100 issuch that the lock plates on their upper surfaces will fit underneaththe retainer 110, while the diametrically opposite portions of theselock plates are somewhat wider so that the lower edge of lock plate 100most immediately adjacent retainer 110 would engage the retainer if thelock plate or the retainer were moved sufficiently axially. The upperportion of lock plate 96 extends radially outward a somewhat greaterdistance so that it is of greater total radius than the inner radius ofretainer 110. A ramp member 112, which also may be a snap ring, islikewise installed in recess 58 and is positioned between retainer 110and the piston head 54. The ramp member is positioned at an obliqueangle to the axis of the piston and the actuating shaft, with the upperportion of the ramp, as seen in FIG. 1, being closer to the piston headthan its lower portion. The lower sides of all of the lock plates are ofinsufficient radial width to engage the lower portion of ramp member112. However, the upper portion of lock plate 96 is of sufficient radialwidth so as to be engageable with ramp 112 as more particularlydescribed below. A thrust member 114, which may be a thrust washerassembly or a needle bearing type thrustmember, is positioned againstthe inner side of the piston head 54 and has its outer element 1'16engageable by the lower corner of lock plate 96, this lower cornerconstituting a force point 118.

The outer surface of piston head 54 engaging backing plate 38 of brakepad assembly 26 is provided with one or more recesses 120 which areengaged by lugs or bosses 122 formed on or struck from backing plate 38so as to ,prevent any substantial rotational movement of piston 40 incylinder 42. As can better be seen in FIG. 2, the backing plates 36 and38 extend circumferentially a somewhat greater distance than do thelinings and 22. The backing plates are provided with ears 124 and 126 atopposite circumferentially extending ends thereof, these ears engagingthe side surfaces 128 and 130, respectively, of the bridge section 30 ofthe caliper frame 28. Thus the brake torque is transmitted from thebrake pad assemblies to the caliper frame by the brake shoe ears 124 and126, and none of the torque is transmitted to the caliper frame throughthe piston 40. This arrangement also prevents any substantialcircumferential movement of the brake show assembly 26, and consequentlybosses 122 and recesses 120 prevent any substantial rotational movementof the piston.

During normal brake operation, hydraulic pressure is introduced intopressure chamber 60 in order to actuate the brake for service operation.The pressure acts on piston 40 to move the piston toward disc 14,engaging brake lining 22 with the friction surface 18 of the disc. Atthe same time the hydraulic reaction causes the caliper assembly to moverightwardly as seen in FIG. 1,

if a sliding caliper arrangement is used, so that leg 28 of the caliperframe 30 forces the friction lining 20 into frictional engagement withthe friction surface 16 of disc 14, thereby applying braking force tothe disc. The leftward movement of piston 40, with the brake properlyadjusted, usually results in so little movement as to require noadditional adjustment. However, upon initial installation of the brakelinings or upon sufficient brake lining wear, this movement will be suchthat retainer 110 will engage the lower edge of lock plate 100, causingthe lock plates to slide on the enlarged section of actuating shaft 64leftwardly relative to that shaft. Upon brake release, when the piston40 tends to withdraw into cylinder 42, the piston will move only asufficient amount to engage the thrust element 116 with the lower leftedge of lock plate 96 at force point 1 18. This engagement causes all ofthe lock plates of the lock plate pack to lock on shaft enlarged section80, preventing further movement of piston 40 into cylinder 42 and towardactuating shaft 64. Thus the piston is permitted to retract only theamount of the predetermined clearance between force point 118 and thethrust element 116.

When the'brake is applied manually the cable load on lever 72 isincreased, causing the lever to move arcuately to rotate actuating shaft64. Due to the action of the ball-ramp actuator 88, the shaft also movesaxially inward in relation to the cylinder 42, toward piston head 54.The force point 118 of the lock plate pack, and particularly of lockplate 96, contacts the thrust element 116, which in turn causes thepiston 40 to move outwardly against the brake pad assembly 26. The lockplate pack remains axially stationary in relation to the actuating shaftdue to the locking action created between the outer diameter of theshaft enlarged section 80 and the close fitting openings 102, 104 and106 in the lock plates 96, 98 and 100. Therefore, as the lining wears,the parking lever continues to operate within a fixed range. Since thebrake will be adjusted each time it is hydraulically actuated, and sinceservice brake operations normally occur numerous times between parkingbrake operations, the brake is always sufficiently closely adjusted topermit full parking brake operation.

When the piston 40 must be reset to its initial position because ofinstallation of new linings, the old brake shoe assembly 26 is removedand the piston is rotated approximately to so that the ramp 112 has asection moving axially toward the upper left edge of lock plate 96. Whenthe ramp engages the upper left lock plate edge, and moves it slightlyaxially the lock plates are released from the shaft and are held in areleased or unlocked position so that they allow the lock plate pack tobe pushed toward the cylinder base wall 62 as the piston is pushed inthat direction. After the brake pad assemblies with new linings areinstalled and the brake is again placed in operation, the firsthydraulic actuation of the brake will cause the lock plates to again bepositioned so as to maintain adjustment of the piston and thereforeminimum clearance between brake shoes 20 and 22 in relation to theirrespective disc friction surfaces 16 and 18, upon brake release.

What is claimed is: 1. -In a disc brake actuator and adjuster mechanism:a pressure actuated member reciprocably movable in brake actuating andrelease directions; a mechanically actuated member axially aligned withsaid pressure actuated member and reciprocably movable in brakeactuating and release directions;

one-way lock means mounted on one of said members and operativelyengageable with the other of said members to selectively slide inrelation to one of said members when the axial relative movement of saidmembers, generated by movement of either member is in an openingdirection relative to the other member, said lock means beingoperatively engageable with the other of said members to lock saidmembers in axial force transmitting relation therebetween upon apredetermined amount of axial relative movement of said membersgenerated by movement of either member in a closing direction relativeto the other member;

normally inactive member reset means for said oneway lock means mountedon one of said members and actuated by rotational movement of the onemember on which it is mounted to engage said lock means and prevent thelocking thereof and permit relatively closing axial movements of saidmembers to reset said members; and means associated with the one of saidmembers on which said reset means is mounted and normally preventingrotatable movement thereof and when released permitting at leastsufficient rotational movement thereof to actuate said reset means.

2. A brake actuator and adjuster mechanism comprising:

a housing having a wheel cylinder formed therein and defined by acylinder wall and a base;

a brake actuating piston reciprocably received in said wheel cylinderand cooperating with said cylinder wall and base to define a brakeactuating pressure chamber, said piston having a head and a recessedskirt section extending from said head toward said base;

a shaft axially and rotatably movably mounted in said base in axialalignment with said'piston and having an outer end extending outwardlyof said base, an inner end axially aligned with said piston head, andmeans thereon for imparting rotational and axial forces and movementsthereto;

' an annular thrust member on said piston in said recess at said pistonhead and receiving said shaft therethrough;

a resetting ramp member mounted in said piston skirt at an oblique angleto the piston axis and in axially spaced relation to said thrust member;

a retainer member mounted in said piston skirt in axially spacedrelation to said ramp member and on the opposite side thereof from saidthrust member;

and annular lock plate means mounted on said shaft for relative slidingmovement in the axial direction toward said piston head and lockingaction on said shaft for attempted relative sliding movement in theother axial direction;

said retainer engaging one edge of said lock plate means at a firstcircumferentially definite point upon a predetermined amount of movementof said piston and said retainer, under the force of brake actuatingpressure in said pressure chamber, relative to said shaft to cause saidlock plate means to slide axially on said shaft to adjust the pistonposition for brake wear;

said lock plate means operatively engaging said thrust member at theopposite edge at a second circumferentially definite point insubstantial axially parallel alignment with said first circumferentiallydefinite point upon a predetermined amount of axial movement of saidshaft toward said piston head to cause said lock plate means to lock tosaid shaft and act through said thrust member to move said piston in thebrake actuating direction; said ramp member normally being clear of saidlock plate means but by rotation of said piston said ramp member beingpositioned to engage said lock plate means on said opposite edge at athird circumferentially definite point circumferentially spaced on saidlock plate means from said second circumferentially definite point tounlock said lock plate means and said shaft and allow said lock platemeans to be pushed in axially sliding movement relative to said shafttoward said cylinder base by said piston to reset said piston when newlinings are installed.

1. In a disc brake actuator and adjuster mechanism: a pressure actuatedmember reciprocably movable in brake actuating and release directions; amechanically actuated member axially aligned with said pressure actuatedmember and reciprocably movable in brake actuating and releasedirections; one-way lock means mounted on one of said members andoperatively engageable with the other of said members to selectivelyslide in relation to one of said members when the axial relativemovement of said members, generated by movement of either member is inan opening direction relative to the other member, said lock means beingoperatively engageable with the other of said members to lock saidmembers in axial force transmitting relation therebetween upon apredetermined amount of axial relative movement of said membersgenerated by movement of either member in a closing direction relativeto the other member; normally inactive member reset means for saidone-way lock means mounted on one of said members and actuated byrotational movement of the one member on which it is mounted to engagesaid lock means and prevent the locking thereof and permit relativelyclosing axial movements of said members to reset said members; and meansassociated with the one of said members on which said reset means ismounted and normally preventing rotatable movement thereof and whenreleased permitting at least sufficient rotational movement thereof toactuate said reset means.
 2. A brake actuator and adjuster mechanismcomprising: a housing having a wheel cylinder formed therein and definedby a cylinder wall and a base; a brake actuating piston reciprocablyreceived in said wheel cylinder and cooperating with said cylinder walland base to define a brake actuating pressure chamber, said pistonhaving a head and a recessed skirt section extending from said headtoward said base; a shaft axially and rotatably movably mounted in saidbase in axial alignment with said piston and having an outer endextending outwardly of said base, an inner end axially aligned with saidpiston head, and means thereon for imparting rotational and axial forcesand movements thereto; an annular thrust member on said piston in saidrecess at said piston head and receiving said shaft therethrough; aresetting ramp member mounted in said piston skirt at an oblique angleto the piston axis and in axially spaced relation to said thrust member;a retainer member mounted in said piston skirt in axially spacedrelation to said ramp member and on the opposite side thereof from saidthrust member; and annular lock plate means mounted on said shaft forrelative sliding movement in the axial direction toward said piston headand locking action on said shaft for attempted relative sliding movementin the other axial direction; said retainer engaging one edge of saidlock plate means at a first circumferentially definite point upon apredetermined amount of movement of said piston and said retainer, underthe force of brake actuating pressure in said pressure chamber, relativeto said shaft to cause said lock plate means to slide axially on saidshaft to adjust the piston position for brake wear; said lock platemeans operatively engaging said thrust member at the opposite edge at asecond circumferentially definite point in substantial axially parallelalignment with said first circumferentially definite point upon apredetermined amount of axial movement of said shaft toward said pistonhead to cause said lock plate means to lock to said shaft and actthrough said thrust member to move said piston in the brake actuatingdirection; said ramp member normally being clear of said lock platemeans but by rotation of said piston said ramp member being positionedto engage said lock plate means on said opposite edge at a thirdcircumferentially definite point circumferentially spaced on said lockplate means from said second circumferentially definite point to unlocksaid lock plate means and said shaft and allow said lock plate means tobe pushed in axially sliding movement relative to said shaft toward saidcylinder base by said piston to reset said piston when new linings areinstalled.